1. Technical Field
This invention relates generally to in-vitro diagnostics, and more particularly to disposable diagnostic cartridges and apparatus and methods for controlling the functions required to execute an assay on a diagnostic cartridge.
2. Related Art
Diagnostic tests are increasingly being used to determine the state or condition of a biological environment, such as in human healthcare, agriculture, livestock management, municipal systems management, and national defense, by way of example and without limitation. A new market is emerging wherein diagnostic tests are being performed at the point-of-care. The diagnostic test can be complex, requiring multiple fluids and multiple steps to execute an assay. An assay is a sequence of steps or procedures used to measure the presence or absence of a substance in a sample, the amount of a substance in a sample, or the characteristics of a sample. An example of a common and relatively simple point-of-care assay, which can be readily conducted by a layperson, is a blood glucose test. In this test, generally speaking, the blood is mixed with glucose oxidase, which reacts with the glucose in the sample, creating gluconic acid, wherein the gluconic acid reacts with a chemical, typically ferricyanide, producing ferrocyanide. Current is passed through the ferrocyanide and the impedance reflects the amount of glucose present.
Although the aforementioned blood glucose assay is relatively common and simple, many assays are far more complex, in that they require specific fluids, often of differing types and quantities, to be stored and maintained separate from one another for future use on the diagnostic device. These fluids may be, but are not limited to, a buffer solution for dilution, fluids containing antibodies and antigens, microspheres coated with binding agents, cell lysing agents, and other fluids required to manipulate the sample being tested. Diagnostic tests that utilize millifluidic and microfluidic volumes of the fluids are intended to provide an incredibly high degree of specificity, sensitivity, and a precise volume and rate of fluid delivery to achieve as accurate a test result as possible. Nearly all microfluidic tests require the introduction of fluids, control of flow, mixing of fluids and other interactive functions throughout the assay sequence to manipulate the sample being tested and to produce an accurate diagnosis.
Typically, consumable diagnostic devices, meaning the diagnostic device is disposable upon being used, require a complex companion durable hardware device that interfaces with the consumable diagnostic device to execute the test. The durable hardware performs many functions, one of which is to facilitate dispensing the fluids contained in a reservoir or reservoirs on the consumable diagnostic device into microfluidic or millifluidic channels formed within the consumable diagnostic device. Fluids may be contained within a deformable vessel, comprised of a malleable material, typically made from aluminum or a thin foil. Dispensing the fluid from the deformable vessel(s) typically proves challenging to attain the desired flow, including volume and rate of flow. Upon being urged to flow out of the reservoirs, the fluids can flow into a specimen containing reaction chamber. The introduction of the fluids to the reaction chamber requires precision; including flow rate, volume and timing, so as to best replicate the laborious protocols of a laboratory, where precession pipettes are employed. This continues to prove difficult in point-of-care diagnostic devices.
Diagnostic assays requiring fluid management require precise opening and dispensing of fluid from reservoirs, opening and closing of valves, pumping and mixing of fluids and may include the introduction of sensors, including, such as optic, thermal, electrical and magnetic devices used in the preparation and analysis of the diagnostic assay. Regardless, attaining the desired precision; including flow rate, volume and timing, so as to best replicate the protocols of a laboratory continues to prove challenging, particularly if the assay is complex.
Another function performed in diagnostic assays involves the capture and release of chemically and biologically tagged ferrous beads. Ferrous beads are commonly used to facilitate the capture and release and handling of target elements. The fluid containing the target element is combined with a ferrous bead containing a receptor, or tag. The bead binds or links with the target element, at which point a magnet is moved into close proximity to the beads, thereby immobilizing the beads within a chamber or zone. A rinse fluid flushes away the non-specific elements, leaving the target elements bound to the beads. At this stage the magnet may be released, allowing the beads to pass to a different zone on the consumable device, thus allowing subsequent processing. This action requires movement of the magnets, which if not conducted properly, can have an adverse impact on the test results.
Another function performed in diagnostic assays involves not only the pumping or movement of fluids, but also the mixing of fluids, which again, if not performed precisely, can have an adverse impact on the test results.